In order to best utilise resources of cellular networks, it is beneficial for network operators to balance the traffic and signalling load between the cells. Once a particular cell has used up its resources at a particular time, that cell becomes congested and is unable to manage communications with any further mobile devices (UEs).
Methods for load balancing between cells are well known. U.S. Pat. No. 5,796,722 (Motorola), which is incorporated herein by reference, describes a method in which the effects of congestion are managed by monitoring the activity on different carriers and, when a carrier becomes congested, handing over call traffic from that carrier to a different carrier.
The objective of load balancing is to maximise system capacity by distributing traffic from congested cells to more lightly loaded cells. By handing over a UE to a more lightly loaded cell, it is hoped that the Quality of Service (QoS) experienced by that UE will improve, even though it is not now connected its preferred cell, due to the increased resources that can now be allocated to that UE.
However, although network performance can be improved by load balancing handovers of UEs between cells, such handovers will result in UEs no longer being connected to the optimum cell (i.e. that with the lowest pathloss to the UE). When a UE is not connected to the optimum cell, excess uplink (UL) and downlink (DL) interference to neighbouring cells can be caused by the need to transmit additional power in order to overcome the higher pathloss. The heavily loaded cell will have few or no idle radio resources available, so it would be advantageous to allocate resources which minimise interference to users remaining on the original cell.